[S390] cio: Device status validity.

Only accumulate device status field in irb if it is valid.

Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

drivers/s390/cio/device_status.c

@@ -263,7 +263,11 @@ ccw_device_accumulate_irb(struct ccw_device *cdev, struct irb *irb)
 		cdev_irb->scsw.cpa = irb->scsw.cpa;
 	/* Accumulate device status, but not the device busy flag. */
 	cdev_irb->scsw.dstat &= ~DEV_STAT_BUSY;
-	cdev_irb->scsw.dstat |= irb->scsw.dstat;
+	/* dstat is not always valid. */
+	if (irb->scsw.stctl &
+	    (SCSW_STCTL_PRIM_STATUS | SCSW_STCTL_SEC_STATUS
+	     | SCSW_STCTL_INTER_STATUS | SCSW_STCTL_ALERT_STATUS))
+		cdev_irb->scsw.dstat |= irb->scsw.dstat;
 	/* Accumulate subchannel status. */
 	cdev_irb->scsw.cstat |= irb->scsw.cstat;
 	/* Copy residual count if it is valid. */